We propose to study the relationship of methane producing bacteria to human dental disease. In preliminary experiments enrichment cultures and isolated strains have been obtained from dental plaque in a variety of periodontal patients. Long term objectives are to understand the ecological relationships of the methanogens in this novel, heretofore unstudied ecosystem, and to examine the effects of the bacteria on the human host. Specific aims here are to: (1) Determine if the presence of methanogens in dental plaque is principally in cases of diseased conditions; (2) characterize the isolated methanogens using microbiological and immunological techniques (3) examine the ability of methanogens to modify the metabolism of heterotrophic bacteria in mixed cultures obtained from dental plaque. Samples of subgingival plaque will be anaerobically transferred to methanogen medium, and enrichment cultures obtained using H2 + CO2 as a carbon and energy source. Pure cultures will be obtained by plating anaerobically onto Gellrite plates and incubating under H2/CO2. Immunological analysis of enrichments and pure cultures, as well as nutritional studies will allow characterization of the methanogens present; preliminary findings suggest we may discover novel organisms. By sampling a wide range of subjects and using appropriate controls and statistical techniques we will be able to conclude if methanogens are correlated with periodontal disease.